For the pudding, preheat the oven to 200C/400F/Gas 6. Butter the pudding basins really well with a third of the softened butter, then dust with the plain flour.
Place the dates and the water in a saucepan and bring to the boil.
Whisk the remaining butter and the sugar together in a large bowl using an electric beater until light and fluffy. Gradually add the golden syrup, treacle, vanilla extract and eggs to the mixture and continue beating. Turn the beaters down to a slow speed and add the self-raising flour, a spoon at a time. Beat until all the ingredients are well combined.